Doppler-Radar: Radial winds, Time Sequence: 15 Min, 01 March 2008     

This chapter contains a time sequence of radial winds from the Doppler radar near Frankfurt. Although each image contains the legend you may click upon the key symbol (above) for better reading.

The radar equipment of the DWD covers wind speeds of -31.5 m/s (blueish pixels approaching) and +31.5 (redish pixels, streaming away from the station). Higher wind speeds are displayed by folding. In that case you have to subtract or to add 63 m/s. For example, wind speeds of -35 m/s are displayed as violet pixels because (-35 m/s+63 m/s)=28 m/s which is displayed in violet (according to the legend for 24.5 to 31 m/s). Analogous, positive wind speeds of 35 m/s are shown as blue pixels because (35-63)m/s=-28 m/s that is displayed as blue (according to the legend). Folding is likely if you do not find a zero-line (light blue) between the redish and blueish colours. This is the case in this image northwest and southeast of Frankfurt.

This image reveals high radial winds of -31.5 to -38.5 m/s (west of Frankfurt) and 31.5 to 38.5 m/s (east of this station). The light blue areas are orientated almost perpendiculary, i.e., indicating almost west wind.

The radial wind speeds remained almost unchanged.

Also this images does not deliver new information.

Now, we recognise north of Frankfurt a clear wind direction's change from West to Northwest indicating the position of the convective line. We derive (just above the legend of the image) a strong increase of the radial wind from between -17.5 and -24.5 m/s to -31.5 to -38.5 m/s. This was probably due to the heavy downbursts during the convective line's passage.

During convective situations Doppler images are also very useful for estimating gusts because the wind speed in about 2 km is rather similar to the gusts. Doppler images are a good completion to surface measurements due to the partly coarse measurement network.

The convective line approached to Frankfurt. We find again high radial winds during its passage. A further wind maximum can be found at the upper left corner. In this area strong radial winds, however, from West-Northwest were measured.

The convective line was about 30 km north of Frankfurt. Again, we find the two maxima of the radial wind (near the convective line and northwest of it). The upper right quadrant is difficult to interpretate. We recognise increasing positive wind speeds (equivalent to air streaming away from the radar). Going more to the south from there we see areas of negative values with decreasing amounts, showing probably increasing radial wind up to 45 to 52 m/s. The small line with "dotted" light blueish pixels between the red and violet area might be due to extreme wind speeds connected to microscale structures (directly at the convective line). If we trust these values we would get radial winds between 57.5 and 62 m/s.

The convective line was probably very near to the radar location.

The convective line was a few kilometres south of the radar station. We still see maximum radial wind speeds between 38 and 45 m/s in 2 km height (east of Frankfurt). The origin of the small yellow and red pixels is not clear and might be due to erroneous pixels.

The convective line was in the meanwhile about 40 km south of Frankfurt. The radial winds remained still high with similar values.

No significant changes occured.

The radial winds kept still as high as in the images before (around 40 m/s in 2 km heigt, i.e, about 80 knots).

The Doppler radar measures radial winds of moving hydrometeors. Because in the northern parts of this images only a few hydrometeors existed we get only a few information about radial winds from there.

The convective line left the domain of this Doppler radar station. However, the radial winds remained still high.